Fluidized bed apparatus

ABSTRACT

A plunger pipe (40) connectable to a gas source projects axially from above into a container (10) which is rotationally symmetrical with respect to a vertical container axis (A). A dish (16) is arranged below the plunger pipe (40) to deflect the gas supplied through the plunger pipe (40) in upward direction so as to move the material (C) contained in the container (10). In an upper area of the container (10) a deflector shield (56) is arranged around the plunger pipe to deflect the material (C) entrained upwardly by the gas in outward direction. A gas outlet opening (26) is disposed above the deflector shield (56) which is permeable to gas at least in some areas. The apparatus is suitable for mixing, drying, granulating, pelleting, polishing, and/or coating pulverous or granular material.

The invention relates to a fluidized bed apparatus for mixing, drying,granulating, pelleting, polishing and/or coating pulverous or granularmaterial, comprising a container which is at least apparoximatelyrotationally symmetrical with respect to an at least approximatelyvertical container axis,

a plunger pipe projecting axially from above into the container andconnectable to a gas source,

a dish disposed below the plunger pipe to deflect gas entering throughthe plunger pipe in upward direction so as to move the material in thecontainer, in particular to fluidize it,

a deflector shield disposed at least approximately in rotationalsymmetry all around the plunger pipe in an upper area of the containerto deflect the material entrained upwardly by the gas in outwarddirection,

and a gas outlet opening disposed above the deflector shield.

In a known fluidized bed apparatus of this kind (DE-PS No. 872 928) thedeflector shield is embodied by a circular, substantially flat baffleplate, the outer edge of which is bent obliquely in a downward directionand positioned close to the wall of the container in such manner that anannular gap is formed between the two. The material entrained by the gasin upward direction around the plunger pipe is distributed by thedeflector shield from the center toward all sides like a fountain sothat it will settle again in the container without requiring any specialspace for a bulk material cone forming. The gas flows upwardly aroundthe outer edge of the deflector shield and through the annular gap intothe suction nozzle of a blower by which it is again pressed into thecontainer through the plunger pipe.

This known deflector shield is hardly suited to provide the desireduniform settling of the material. Still less is it possible to obtainthorough and yet gentle circulation of the material. If at all, it isobtainable only with exceptionally easily movable material. If vigorousgas flow is produced to convey specifically heavy material upwardlyalong the outside wall of the plunger pipe, the material will hit thedeflector shield at considerable energy and thus may be alteredundesirably. A strong gas flow is developed in the annular gap betweenthe outer edge of the deflector shield and the container wall and it mayentrain quite considerably quantities of smaller particles of thematerial. If one attempts to avoid the undesired effects of a strong gasflow by letting the gas flow more slowly, then very soon a status willbe established at which it will no longer be possible to conveysufficient quantities of material in upward direction, particularlymaterial which is difficult to treat to that uniform and quick treatmentof the material no longer is obtainable.

It is, therefore, the object of the invention to develop a fluidized bedapparatus of the kind specified such that gentle and, at the same time,quick and uniform treatment of the most varied kinds of pulverous orgranular material will be possible.

This object is met, in accordance with the invention, in that thedeflector shield is permeable to gas at least in individual areas.

In this manner the gas flow which has conveyed the material upwardlyalong the plunger pipe will separate gradually from the material sincethe gas can flow upwardly through the permeable areas of the deflectorshield, rather than being forced to flow as far as into the vicinity ofthe outer container wall and then pass upwardly at rather high velocitythrough an annular gap. The areas of the deflector shield which arepermeable to gas may be so designed and arranged that gas will passthrough them at moderate velocity while the material is being held back,without being damaged, by the deflector shield.

The gas-permeable areas of the deflector shield in accordance with theinvention permit the design of preferred embodiments with which thedeflector shield extends radially outwardly to an upper container edge.

In such embodiments, preferably the deflector shield forms a vaulthaving a circular apex whose apex diameter corresponds at leastapproximately to the mean value of the diameters of the plunger pipe andthe upper container edge. The result of this design of the deflectorshield is that the material carried upwardly by the gas flow along theplunger pipe will be directed gently outwardly and finally downwardly.The flow velocity of the gas which gradually flows out in an upwarddirection is so low that the gas cannot carry any greater quantities ofdust-like particles upwardly from the material and out of the treatmentspace as defined by the deflector shield of the container.

To be permeable to gas, the deflector shield may comprise elongatedrecesses, each having at least an approximately radial longitudinalaxis.

Such recesses each may contain a screen insert bent in Vee along thelongitudinal axis of the recess. The screen inserts also may be sodesigned that the entire deflector shield forms a substantially smoothvault. However, inserts of V-shaped cross section have the advantagethat their effective surface area is greater than that of the associatedrecess. The surface area which is thus increased by the screen insertspermits the gas to leave the treatment space of the fluidized bedapparatus in upward direction at a particularly low velocity.

It is convenient to have a downwardly extending apron delimit eachrecess, particularly if the recesses do not contain screen inserts.

Preferably a fin extending upwardly along the plunger pipe terminatesclose to the longitudinal axis of each recess so as to direct thematerial flowing upwardly into the areas of the deflector shield locatedbetween the recesses. Such fins prevent individual parts of the materialfrom hitting the edges of the screen inserts, if provided. The fins alsomay be so designed as to deflect the material totally out of the area ofthe recesses of the deflector shield so that screen inserts in therecesses may be dispensed with.

Preferably the fins each have a radial extension which progressesgradually along the plunger pipe from the bottom to the top. In thismanner the fins will begin gradually to direct the material which flowsupwardly along the plunger pipe, not giving the material a chance toimpinge on the fins.

If the fins are helical, this will provide the additional advantage offurther improving the circulation and thorough mixing of the material.

In accordance with a variant of the embodiment of the deflector shieldincluding individual oblong recesses, the major part of the deflectorshield is of screen-like structure.

The invention will be described further, by way of example, withreference to the accompanying diagrammatic drawings, in which:

FIG. 1 is an axial section through a first embodiment of a fluidized bedapparatus according to the invention;

FIG. 2 is an axial section through a second embodiment;

FIG. 3 is an axial section through parts of a fluidized bed apparatusaccording to a third embodiment;

FIG. 4 is an axial section through a structural group of FIG. 3;

FIG. 5 is the top plan view belonging to FIG. 4;

FIG. 6 is a supplemented side elevational view of the structural groupshown in FIG. 4; and

FIG. 7 is a section along line VII--VII of FIG. 6, FIGS. 3 to 6 eachpresenting two different variants of the third embodiment, at the rightand left sides.

The fluidized bed apparatus shown in FIG. 1 comprises a container 10which is rotationally symmetrical with respect to a vertical containeraxis A and composed of an annular lower part 12 and a container insert14. The lower part 12 tapers frustoconically in downward direction,opening without any setoff or step into a bowl or dish 16 which likewiseis rotationally symmetrical with respect to the container axis A. Thecontainer 10 is transportable by a lift car 20 of substantiallyconventional design.

The container insert 14 flares upwardly from the lower part 12, at thesame cone angle, reaching its maximum diameter approximately at half theheight of the container level. From that level on, the container insert14 is slightly converging toward a horizontal upper container edge 22.

A jacket 24 which annularly encloses the container insert 14, terminatesin a horizontal plane just below the container edge 22, and includes alateral gas outlet opening 26 is fixed to the lower part 12. The jacket24 is closed at the top by a container lid 28 which forms an arch spacedfrom the container edge 22 and is sealed with respect to the jacket 24by a tubular seal 30.

The jacket 24 and container lid 28 are interconnected by a hinge 32having a horizontal pivot axis and by a piston and clyinder unit 34spaced from the hinge. The connection is such that the container lid 28is pivotable in upward direction into an at least approximately verticalposition.

The container lid 28 comprises a central inlet nozzle 36 from which aplunger pipe 40 is suspended by a hinge 38 so as to be aligned with theinlet nozzle 36 when the container lid 28 is in its closed positionshown. Upon upward pivoting of the container lid 28, the plunger pipe 40becomes displaced upwardly substantially in parallel with itself,approaching the hinge 32 of the container lid.

In its lower end zone the plunger pipe 40 comprises a marginal bead 42formed by the lower end of a substantially rigid shell of the plungerpipe 40. Together with a substantially cylindrical wall 44 of the dish16 into which the plunger pipe 40 is immersed, the marginal bead 42defines an annular space 45.

The dish 16 has a central bottom zone 46 which is formed with an axiallyupwardly protruding tip 48. The bottom zone 46 may be inserted as aseparate structural member in the dish 16, as shown in FIG. 2. In thisevent an outer guide tube 50 is formed at its underside and guided foraxial displacement in an inner guide tube 52 which is fixed to a foot18. A piston and cylinder unit 54 is disposed inside the inner guidetube 52 to permit the central bottom zone 46 to be raised so that itwill at least almost touch the marginal bead 42, uncovering a dischargeopening in the center of dish 16. If the dish 16 is formed in one-piece,as shown in FIG. 1, however, it may comprise a tangentially positioneddischarge nozzle 55 at its bottom, as demonstrated in FIG. 1.

A mushroom-shaped deflector shield 56 is fixed to the plunger pipe 40,slightly spaced below the plane of the container edge 22. As shown inFIG. 1, the deflector shield 56 is formed by a screen-like aperturedsheet of stainless steel and has an outer diameter which is a littlesmaller than half the diameter of the upper container edge 22.

By contrast, in FIG. 2 the deflector shield 56 is largely made ofscreen-like fabric, extending across the entire space between theplunger pipe 40 and the container edge 22 where the outer margin of thedeflector shield 56 is clamped between the one-piece container 10 ofthis embodiment and the container lid 28. In radial section thisdeflector shield 56 forms a circular arc shaped vault. The apex circle57 of the vault which likewise has the shape of a circular arc, and ofwhich two points are to be seen in FIG. 2, has a diameter whichcorresponds approximately to the mean value between the inner and outerdiameters of the screen-like major portion of the deflector shield 56.

As shown in FIG. 1, a plurality of nozzles 58 are installed in the lowerpart 12 of the container 10, offset at regular angular spacings. Theyare directed obliquely inwardly and upwardly and adapted to be suppliedthrough conduits 60 with liquids to moisten, polish, and/or coatmaterial C contained in the container 10. As shown in FIG. 2,corresponding nozzles 58 are installed in the upper portion of themarginal bead 42. They are directed obliquely outwardly and upwardly.

Together with the container lid 28 the container 10 of the fluidized bedapparatus according to FIG. 2 completes the shape of a sphere and,therefore, is adapted to resist relatively high internal pressure, suchas may occur if solvents explode. A container jacket such as shown inFIG. 1 is not necessary with the embodiment according to FIG. 2. Forthis reason the gas outlet opening 26 is formed in the container lid 28.

At diametrically opposed locations two axle journals 84 project awayfrom the container 10 shown in FIG. 2, their common axis constituting ahorizontal pivot axis D. The axle journals 84 are supported in posts 86and the latter are fixed to a lift car 20 which otherwise corresponds tothe one shown in FIG. 1. At one of the posts 86 there is a geartransmission 88 to be driven manually so as to pivot the container 10together with the container lid 28 about the horizontal pivot axis D,for instance, if thorough cleaning is required when there is a change inproduct.

According to FIGS. 1 and 2 the container 10, including the associateddish 16 as well as the lid 28 are made of metal, preferably stainlesssteel. FIG. 3, on the other hand, shows an embodiment of the fluidizedbed apparatus having the container 10 and its dish 16 made in one pieceof glass and also having a glass lid 28.

The deflector shield 56 according to FIGS. 3 to 7 is made of stainlesssteel and forms a higher vault, as compared to FIG. 2, which is almost asemicircular vault in radial section. Elongated recesses 90 are cut inradial direction in this vault. If one interconnects the radially innerand outer ends of each recess 90, an approximately horizontallongitudinal axis 92 is obtained. The longitudinal axes 92 of allrecesses 90 lie in a common horizontal plane.

In the case of the variant shown in the right half of FIGS. 3 to 6 eachrecess 90 contains a screen insert 94 which is tightly connected to theedges of the recess and bent in V-shape along the longitudinal axis 92.The space enclosed by each screen insert 94 and open to the top has aconfiguration similar to a slice of an orange. The variant shown at theleft in FIGS. 3 to 6 does not have the recesses 90 lined with screeninserts but instead defined all around by a downwardly extending apron96 each.

Fins 98 are formed at regular angular spacings at the outside of theplunger pipe 40. They begin a short distance above the annular space 45and extend up to one of the longitudinal axes 92. In radial direction,the fins 98 have a height zero at their lower ends, while at their upperends the height corresponds approximately to one fourth of the length ofthe respective longitudinal axis 92. The fins 98 may be helically formedin the same sense, as shown particularly in FIGS. 6 and 7. At any ratethe fins 98 have such an outline that they will deflect upwardly flowingmaterial C from the recesses 90.

All embodiments shown have in common that, in operation, a gas, such asheated, dry air is directed from above into the plunger pipe 40, thenflows downwardly through the same at a velocity of, for instance, 20 to40 m/sec. to be deflected in the dish 16 by about 180° and directedupwardly in the annular space 45. The flow velocity of the gas in thenarrowest region of the annular space 45 is at least 20 m/sec.,preferably between 30 and 60 m/sec. The gas then flows upwardly in arather restricted area around the plunger pipe 40 or its shell,fluidizing the material C contained in the container 10 at least in thisarea.

With both variants of the embodiment according to FIGS. 3 to 7 theupwardly flowing material C is channelled by the fins 98 and given ascrew-thread-like motion if the fins are helical.

Part of the gas will flow around and the other part through thedeflector shield 56, depending on the particular design thereof (FIG.1), or all of the gas will flow through the deflector shield (FIGS. 2 to7). The gas leaves the container 10 through the gas outlet opening 26,while the flowing material is deflected outwardly by the deflectorshield 56 and then flows down along the wall of the container 10, to becaught once more by the gas stream close to the upper edge of the dish16, and entrained upwardly in a central hose-like flow formation.

Upon treatment of the material C, the container 10 is emptied by openingthe discharge nozzle 55, shown in FIG. 1, and pneumatically conveyingthe material C out of the container or by lifting the central bottomzone 46 of the embodiment shown in FIG. 2 so that the material C maytrickle down by itself. With the embodiment according to FIG. 2 it isalso possible to dump the material C out of the container 10 uponopening of the container lid 28 with corresponding upward pivoting ofthe deflector shield 56. With the embodiment according to FIGS. 3 to 7the container 10 is emptied in the same manner.

I claim:
 1. A fluidized bed apparatus for mixing, drying, granulating,pelleting, polishing and/or coating pulverous or granular material,comprising:a container, which is at least approximately rotationallysymmetrical with respect to an at least approximately vertical containeraxis, and which has an upper edge; a plunger pipe projecting axiallyfrom above into the container and connectable to a gas source; dishmeans disposed below the plunger pipe for deflecting gas enteringthrough the plunger pipe in an upward direction so as to fluidizematerial disposed within the container; a deflector shield which is atleast approximately rotationally symmetrical all around the plunger pipeand which is disposed in an upper area of the container, for deflectingmaterial, entrained upwardly by gas, in an outward direction, whereinsaid deflector shield has elongated recesses, each having an at leastapproximately radial longitudinal axis, said recesses each containing ascreen insert to be permeable to gas at least in individual areas, andwherein said deflector shield forms and arc shaped vault which extendsfrom said plunger pipe radially outwardly to the upper edge of saidcontainer, said vault having a circular apex, the apex diameter of whichcorresponds at least approximately to the mean value of the diameters ofthe plunger pipe and the upper container edge; and a gas outlet openingdisposed above the deflector shield.
 2. The fluidized bed apparatus asclaimed in claim 1, wherein said screen inserts are bent in V-shapealong the longitudinal axis of the associated recess.
 3. The fluidizedbed apparatus as claimed in claim 2, wherein each recess is defined by adownwardly extending skirt.
 4. The fluidized bed apparatus as claimed inclaim 1, comprising a plurality of fins extending upwardly along theplunger pipe, each fin terminating close to the longitudinal axis of oneof the recesses so as to direct the material flowing upwardly into theareas of the deflector shield located between the recesses.
 5. Thefluidized bed apparatus as claimed in claim 4, wherein each fin extendsradially outwardly from said plunger pipe a distance that increasesgradually from bottom toward top.
 6. The fluidized bed apparatus asclaimed in claim 5, wherein said fins are helical.
 7. The fluidized bedapparatus as claimed in claim 4, wherein said fins are helical.
 8. Afluidized bed apparatus for mixing, drying, granulating, pelleting,polishing and/or coating pulverous or granular material, comprising:acontainer, which is at least approximately rotationally symmetrical withrespect to an at least approximately vertical container axis, and whichhas an upper edge; a plunger pipe projecting axially from above into thecontainer and connectable to a gas source; dish means disposed below theplunger pipe for deflecting gas entering through the plunger pipe in anupward direction so as to fluidize material disposed within thecontainer; a deflector shield which is at least approximatelyrotationally symmetrical all around the plunger pipe and which isdisposed in an upper area of the container, for deflecting material,entrained upwardly by gas, in an outward direction, wherein saiddeflector shield has elongated recesses, each having an at leastapproximately radial longitudinal axis, to be permeable to gas at leastin individual areas, wherein each recess is defined by a downwardlyextending skirt, and wherein said deflector shield forms an arc shapedvault which extends from said plunger pipe radially outwardly to theupper edge of said container, said vault having a circular apex, theapex diameter of which corresponds at least approximately to the meanvalue of the diameters of the plunger pipe and the upper container edge;and a gas outlet opening disposed above the deflector shield.